The use of silver nanoparticles (AgNPs) in consumer products is increasing drastically and their potential environmental impacts on aquatic organisms from bacterial communities to vertebrates are not well understood. This study reports on changes in marine bacterial richness using denaturing gradient gel electrophoresis (DGGE), and overall community abundance determined by flow cytometry in marine microcosms exposed to polymer-coated AgNPs (20±5 nm) and ionic silver (Ag(+)). Our study clearly demonstrated that at low concentrations (5 and 50 μg L(-1) total silver), un-aggregated polymer-coated AgNPs and dissolved Ag(+) contamination produced similar effects: a longer lag phase suggesting an adaptation period for microorganisms. As richness decreased in the treated samples, this longer lag phase could correspond to the selection of a fraction of the initial community that is insensitive to silver contamination. Polymer-coated AgNPs preserved their bactericidal properties even under the high ionic strength of estuarine waters.
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